Polymerization of cyclic esters



United States Patent 3,921,314 lOLYMTERiZATIGN OF CYCLIC ESTERS EugeneF. Cox and Fritz Hostettler, Charleston, W. Va., assignors to UnionCarbide Corporation, a corporation of New York No Drawing. Filed Dec. 3,1959, Ser. No. 856,910 14 Claims. (Cl. 260-783) This invention relatesto a process for polymerizing cyclic esters and to the productsresulting therefrom.

The most generally familiar works on the polymerization of lactones arethe now classical investigations of W. H. Carothers. For instance,Carothers was able to polymerize delta-valerolactone topoly-delta-valerolactone by heating at 8085 C. for a period of about 13days, or by contacting delta-valerolactone with potassium carbonatecatalyst at a temperature of 80-85 C. for a period of about days. Theresulting polymers were soft waxes possessing average molecular weightsof approximately 2000 which had relatively low thermal stabilities. Theliterature reports that attempts to polymerize gamma-butyrolactone havebeen unsuccessful, and the corresponding polyester is not known. In1934, there was reported the preparation of poly-epsilon-caprolactone byheating epsilon-caprolactone at about 150 C. for a period of 12 hours,or by contacting epsilon-caprolactone with potassium carbonate at about150 C. for a period of 5 hours. The resulting epsiion-caprolactonepolymers had melting points of about 5355 C. and average molecularweights of about 4000. The polymers were hard, brittle waxes which couldnot be cold-drawn into fibers. Bischofi and Walden described thetransformation of glycolide under the influence of heat or a trace ofzinc chloride into a polymeric solid melting at 220 C. On beingdistilled in a vacuum it was reconverted to the monomer melting at 8687C. The literature also reports the polymerization of lactide at elevatedtemperatures to a resinous mass. A similar effect is also obtained atrelatively lower temperatures by employing potassium carbonate as thecatalyst.

In a broad aspect the present invention is directed to the process forpolymerizing monomeric cyclic esters in contact with a Group 1Ametal-containing catalyst to produce useful polyester products, both thecyclic ester reagents and the catalysts being described hereinafter in amore appropriate section. The average molecular weights of the resultingpolymers can range from about several hundred to about several thousand.The various homopolymers, copolymers, and terpolymers prepared by thepractice of the instant invention are highly useful products as willbecome apparent at a later section herein. In addition, thepolymerization reaction can be conducted at lower temperatures and atfaster polymerization rates heretofore unattainable in lactonepolymerization art.

Accordingly, one 'or more of the following objects will be achieved bythe practice of this invention.

It is an object of this invention to provide a novel process forhomopolymerlzing monomeric cyclic esters to produce useful homopolymers.It is another object of this invention to provide a novel process forpolymerizing an admixture containing at least two different monomericcyclic esters to'produce useful polymers. A further object of thisinvention is to prepare lactone polymers having a high degree of utilityand application in the cosmetic, wax, polish, molding, coating, fiber,film,

"ice

etc., fields. Other objects will become apparent to those skilled in theart in the light of the instant specification.

In one embodiment the monomeric cyclic esters employed in thepolymerization process of this invention can be characterized by thefollowing formula:

wherein each R, individually, can be hydrogen, alkyl, aryl, alkaryl,aralkyl, cycloalkyl, halo, haloalkyl, alkoxyalkyl, alkoxy, aryloxy, andthe like; wherein A can be an oxy (O) group, a thio (S) group, adivalent saturated aliphatic hydrocarbon group, and the like; wherein xis an integer from 1 to 15 inclusive; wherein y is an integer from 1 to15 inclusive; wherein z is an integer having a value of zero or one;with the provisos that (a) the sum of x+y+z cannot equal 3, (b) thetotal number of atoms forming the cyclic ester ring does not exceed 18,preferably does not exceed 9, (c) the total number of organicsubstituents (such as those described for the R variables) attached tothe carbon atoms contained in the cyclic ester ring does not exceed 4,preferably does not exceed 3, (d) from 2 to 4 continuously linked carbonatoms contained in the cyclic ester ring can represent a portion of asaturated cycloaliphatic hydrocarbon nucleus which contains from 4 to 10ring carbon atoms, and (e) the four R variables attached to any twoadjacent carbon atoms contained in the cyclic ester ring can represent aportion of a fused aromatic hydrocarbon nucleus.

With reference to Formula I supra, illustrative R radicals include,among others, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,t-butyl, amyl, the hexyls, the heptyls, the octyls, dodecyl, octadecyl,phenyl, benzyl, tolyl, xylyl, ethylphenyl, butylphenyl, phenethyl,phenylpropyl, phenylbutyl, cyclopentyl, 2-propylcyclohexyl, cyclohexyl,Z-methylcyclohexyl, cycloheptyl, chloromethyl, chloroethyl, bromopropylbromobutyl, chloro, fiuoro, bromo, iodo, methoxyrnethyl, ethoxyethyl,propoxymethyl, butoxypropyl, methoxy, ethoxy, n-propoxy, n-butoxy,isopentoxy, n-hexoxy, Z-ethylhexoxy, 3-methyloctoxy, decoxy, dodecoxy,octadecoxy, phenoxy, ethylphenoxy, propylphenoxy, dimethylphenoxy,phenylpropoxy, and the like. It is preferred that each R, individually,be hydrogen, alkyl, and/or alkoxy, and preferably still, that each R,individually, be hydrogen, lower alkyl, e.g., methyl, ethyl, n-propyl,isobutyl, and/or lower alkoxy, e.g., methoxy, ethoxy, propoxy, n-butoxy,and the like. It is further preferred that the total number of carbonatoms in the substituents attached to the cyclic ester ring does notexceed twelve. Cycloalkyl and lower alkylsubstituted cycloalkyl radicalswhich have from 5 to 7 carbon atoms in the cycloaliphatic nucleus alsoare preferred.

In the discussion of the generic class of monomeric cyclic esters(Formula I) contemplated in the process of the invention, five provisosenumerated from (a) through (e) have been set forth. Proviso (a) statesthat the sum of x+y+z cannot be a number equal to three. This provisoexcludes cyclic ester compounds which contain five atoms in the ringsuch as, for example,

a gamma-butyrolactone Prior art attempts to polymerizegamma-butyrolactone and the substituted gamma-butyrolactones have beenunsuccessful. Attempts to polymerize the cyclic esters, e.g.,gamma-butyrolactones, beta-oxa-gamma-butyrolactones, and the like, inthe process of this invention likewise have failed. One would postulatethat the thermodynamic stability of these monomeric cyclic esters whichcontain five atoms in the lactone ring is much greater than thecorresponding polymers, and that the free energy of interconversion isexceedingly low. Proviso (c) states that the total number of organicsubstituents attached to the carbon atoms contained in the cyclic esterring should not exceed four, and preferably should not exceed three. Ithas been observed that when the totalnumber of organic substituents onthe cyclic ester ring approached four or more, then the polymerizabilityof the cyclic ester monomer in the process of the invention diminisheddrastically. Proviso states that from 2 to 4 continuously linked carbonatoms contained in the cyclic ester ring can represent a portion of asaturated cycloaliphatic hydrocarbon nucleus which contains frorn4 toring carbon atoms such as, for example, a saturated cycloaliphatichydrocarbon nucleus derived from cycloalkane, alkyl-substitutedcycloalkane, cyolobutane, cyclopentane, cyclohexane, cycloheptane,cyclooctane, methylcyclopentane, methylcyclohexane, and the like. Thus,for example, the following illustrative cyclic esters would be includedin this proviso:

. CH, 2-oxa-5,7,7-trimethylbieyclo [4.1.1] octan3-one 2-oxabicyclo[3.2.2 nonan-3-one Proviso (e) states that the four R variables attached toany two adjacent carbon atoms contained in the cyclic ester n'ng canrepresent a portion of a fused aromatic hydrocarbon nucleus, that is, anaromatic nucleus derived from benzene, alkylbenzene,-methylbenzene,propylbenzene, naphthalene and the like. To illustrate this proviso,

the following compound is depicted structurally.

2,3,4,5-tetrahydro-2-keto-benzoxepin In the structurally depictedcompound immediately above,

the four R variables which were attached to the carbon atoms designatedby numerals 6 and 11 now represent a portion of the fused benzene ring,namely the carbon W. H. Carothers, G. L. Borough, and F. J. van Natta,Jour. Amer. Chem. $00., 54, 761 (1932).

atoms designated by the numerals 7, 8, 9, and 10. The following compoundfurther illustrates proviso (e).

2 (2-hydroxymethylpheny1) benzene carboxylic acid lactone Representativemonomeric cyclic esters which can be employed as starting materials inthe method of the invention include, for example, beta-propiolactone,deltavalerolactone, epsilon-caprolactone, 7-hydroxyheptanoic acidlactone, S-hydroxy octanoic acid lactone, 12 -hydroxydodecanoic acidlactone, 13-hydroxytridecanoic acid lactone, l4-hydroxytetradecanoicacid lactone, 15-hydroxypentadecanoic acid lactone,16-hydroxyhexadecanoic acid lactone, 17-hydroxyheptadecanoic acidlactone; the alpha, alpha-dialkyl-beta-propiolactones, e.g., alpha,alpha-dimethyl-beta-propiolactone, alpha,alpha-diethyl-beta-propiolactone, alpha,alpha-dipropyl-beta-propiolactone, and the like; themonoalkyl-delta-valerolactones, e. g., the monomethyl-, monoethyl-,monoisopropyh, monobutyl-, monohexyh, monodecyl-, andmono-dodecyl-delta-valerolactones and the like; thedialkyl-delta-valerolactones in which the two alkyl groups aresubstituted on the same or difierent carbon atoms in the cyclic esterring, e.g., the dimethyl-, diethy1-, diisopropyl-, dipentyl-, anddi-n-octyldelta-valerolactones, and the like; the monoalkyl, dialkyl-,or trialkyl-epsilon-caprolactones, e.g., the monomethyl-, monoethyl-,monoisopropyl-, monohexyl-, mono-n-octyldimethyl-, diethyh,di-n-propyl-, diisobutyh, di-n-hexyl-, trimethyl-, triethyl-, andtri-n-propyl-epsilon-caprolactones, and the like; the monoalkoxyanddialkoxy-deltavalerolactones and epsilon-caprolactones, e.g.,monomethoxy-, monoethoxy-, monoisopropoxy-, dimethoxy-, dieth oxy-, anddibutoxy-delta-valerolactones and epsilon-captolactones, and the like.Further illustrative cyclic esters include 3-ethyl-2-keto-1,4-dioxane,gamma(1-isopropyl-4- methylcyclohexyl)-epsilon-caprolactone,3-bromo-2,3,4,5- tetrahydrobenzoxepin 2 one, 2-t(2-hydroxyphenyl)benzenecarboxylic acid lactone, lO-hydroxyundecanoic acid lactone,2,5,6,7-tetrahydrobenzoxepin-Z-one, 9-oxabicyclo- [5.2.2]undecan 8 one.4-oxa-14-hydroxy-tetradecanoic acid lactone, alpha,alpha-bis(chloromethyl)propiolactone, 1,4-dioxane-2-one,3-n-propyl-2-keto-1,4-dioxane, 3-(2- ethylhexyl)-2-keto-1,4-dioxane, andthe like. Illustrative subclasses of cyclic esters which are eminentlysuitable in the process of the instant invention include theunsubstituted lactones and the oxalactones which contain from six toeight atoms in the lactone ring, preferably deltavalerolactone,epsilon-caprolactone, the keto-dioxanes, and the like; themonoand,polyalkyl-substituted lactones and oxalactones which containfrom six to eight atoms in the lactone ring, preferably the monoandpoly-lower alkyl-delta-valerolactones, epsilon-caprolactones, and theircorresponding oxalactones wherein the alkyl substituents(s) containsfrom 1 to 4 carbon atoms, and the like; and the monoandpoly-alkoxy-substituted lactones and oxalactones which contain from sixto eight atoms in the lactone ring, preferably the monoand poly-loweralkoxy-delta-valerolactones, epsilon-caprolactones, and theircorresponding oxalactones wherein the alkoxy substituent(s) containsfrom 1 to 4 carbon atoms.

The unsubstituted and substituted delta-valerolactones,epsilon-caprolactones, zeta-enantholactones, and higher memberedlactones, e. g., monoand polyalkyl-substituted delta-valerolactones,monoand polyalkoxy-substituted delta-valerolactones,'monoandpolycycloalkyl-substituted delta-valerolactones, aryl-substituteddelta-valerolactones, monoand polyhaloalkyl-substituteddelta-valerolactones, monoand polyalkyl-substitutedepsilon-caprolactones,

monoand polyalkoxy-epsilon-caprolactones, aryl-substitutedepsilon-caprolactones, monoand polyhaloalkylsubstitutedepsilon-caprolactones, monoand polyalkylsubstitutedzeta-enantholactones, and various other lactones described previouslycan be prepared by reacting the corresponding cyclic ketone with ananhydrous solution comprising peracetic acid and acetone. It isdesirable to add the peracetic acid solution to an excess of ketone,e.g., 5 to 1 molar ratio of ketone to peracetic acid, in a still kettlemaintained under reflux. The pressure can be adjusted so as to provide akettle temperature of, for example, about 70 C. Acetone, acetic acidby-product, and minor amounts of ketone can be continuously removedthroughout the addition period. Subsequently, the lactone product can'berecovered from the still kettle by conventional techniques such as bydistillation.

Stoll and Rouv report the preparation of lactones which contain up to 22carbon atoms in the lactone nucleus by a process which comprisescontacting the corresponding terminal hydroxy saturated aliphaticmonocarboxylic acid with benzenesulfonic acid catalyst in boilingbenzene. These authors also report the preparation of other lactonessuch as 14-alkyl-l4-hydroxy-tetradecanoic acid lactone, e.g.,l4-hydroxypentadecanoic acid lactone, and oxa-lS-hydroxypentadecanoicacid lactone, e.g., l2- oxa-lS-hydroxypentadecanoic acid lactone.Palomaa and Tonkola teach the preparation of 3-oXa-6-hydroxyhexanoicacid lactone by heating the corresponding terminal hydroxy saturatedaliphatic monocarboxylic acid. The preparation of 2-keto-l,4-dioxane,3-alkyl-2-keto-1,4-dioxane, polyalkoxy-substituted delta-valero-lactone,monoand polyalkyl-substituted delta-valerolactone,alkoxyalkyl-substituted delta-valerolactone, etc., is recorded byCarothers et al.' The preparation of dialkyl-substituted,dihalo-substituted lactone, e.g., gamma, delta-dibromogamma,delta-dimethyl-delta-valerolactone is reported in the literature byLevina et al. German Pat. No. 562,827 discloses the preparation of2,3,4,5-tetrahydrobenzoxepin- 2-one whereas the literature 9 reports theposition isomer, namely 2,5,6,7-tetrahydrobenzoxepin-Z-one.Cycloalkylsubstituted epsilon-caprolactone, e.g., gamma(l-isopropyl-4-methylcyclohexyl)-epsilon-caprolactone is disclosed by Belov andKheifits. McKay et al. have recorded the preparation ofhalo-substituted, haloalkyl-substituted delta-valerolactone. Theliterature also reports the preparation of various other cyclic esters.

The Group IA metal-containing compound contemplated as catalysts in theprocess of the invention can be characterized by the formula wherein Mrepresents lithium, sodium, potassium, rubidium, or cesium; and whereinA represents an amino radical, a primary amino radical, a secondaryamino radical, or a hydrocarbyloxy radical, e.g., alkoxy, aryloxy,alkenyloxy, cycloalkenyloxy, or cycloalkyloxy radicals, and the like.

lustrative A variables include, among others, amino, methylamino,ethylamino, n-propylamino, n-butylamino, 2-ethylhexylamino,dodeeylamino, octadecylamino, anilino, ortho-, meta-, andpara-toluidino, benzylamino, ortho meta-, and para-xylidino,alpha-naphthylamino, cyclopentylamino, cyclohexylamino,cycloheptylamino, 2- methylcyclohexylamino, 3-n-butylcyclohexylamino,cyclopentenylamino, cyclohexenylamino, dimethylamino, diethylamino,diisopropylarnino, di-n-hexylamino, di-Z-ethylhexylamino,di-n-octylamino, didodecylamino, N-ethyl-propylamino,N-ethyl-m-toluidino, N-propyl-p-xylidino, N-methylanilino,N-phenyl-benzylamino, N-methyl-alpha- 5 Helv. Chim. Acta, 18. 1087(1935). Bern, 66, 1629 (1933).

" See footnote 1.

3 Zhur. Obshchei Khim, 24, 1439 (1954). Ber., 68B 1170 (1935).

J. Gen. Chem. USSR, 27, 1459 (1957). 11 J. Amer. Chem, Soc., 77, 5601-6(1955).

naphthylamino, N-cyclohexyl-heptylamino, l-piperidyl, 1- pyrrolidyl,l-pyrryl, N-carbazolyl, methoxy, ethoxy, npropoxy, isopropoxy, n-butoxy,tert.-butoxy, n-hexoxy, 2- ethylhexoxy, n-octoxy, dodecoxy, octadecoxy,phenoxy, 2- propylphenoxy, 3-n-butylphenoxy, phenethoxy, benzyloxy,ortho-meta-, and para-toloxy, allyloxy, Z-butenyloxy, 2- pentenyloxy,cyclohexenyloxy, cycloheptenyloxy, cyclopentenyloxy, cyclopentyloxy,cyclohexyloxy, cycloheptyloxy, S-n-propylcyclohexyloxy,alkylcyclohexyloxy, alphanaphthyloxy, and the like.

Specific examples of illustrative catalysts include, for instance,sodium methoxide, sodium propoxide, lithium n-butoxide, potassium2-ethylhexoxide, potassium octoxide, sodium dodecoxide, rubidiummethoxide, rubidium nbutoxide, cesium isopropoxide, sodium phenoxide,potassium phenoxide, lithium phenoxide, sodium toloxide, potassiumbenzyloxide, sodium phenethoxide, lithium cyclopentoxide, potassiumcyclohexoxide, sodium allyloxide, potassium Z-butenyloxide, sodiumcyclohexenyloxide, sodium amide, potassium amide, sodium methyl-amide,potassium n-propylarnide, lithium n-butylamide, sodium 2-ethylhexylamide, sodium anilide, potassium beta-naphthylamide, potassiumdiethylamide, lithium diisopropylamide, potassium N-phenyl-ethylamide,potassium di-2- ethylhexylamide, l-piperidylsodium,l-pyrrolidylpotassium, N-carbazolyllithium, and the like.

The catalysts are employed in catalytically significant quantities. Ingeneral, a catalyst concentration in the range of from about 0.001, andlower, to about 10, and higher, weight percent, based on the weight oftotal monomeric feed, is suitable. A catalyst concentration in the rangeof from about 0.01 to about 3.0 Weight percent is preferred. A catalystconcentration in the range of from about 0.05 to about 1.0 weightpercent is highly pretel-red. For optimum results, the particularcatalyst employed, the nature of the monomeric reagent(s), the operativeconditions under which the polymerization reaction is conducted, andother factors will largely determine the desired catalyst concentration.

The polymerization reaction can be conducted over a wide temperaturerange. Depending upon various factors such as the nature of themonomeric reagent(s) employed, the particular catalyst employed, theconcentration of the catalyst, and the like, the reaction temperaturecan be as low as 40 C., and lower, and as high as 250 C., and higher. Asuitable temperature range is from about -20 to about 225 C. A reactiontemperature in the range of from about 0 to about 200 C. is preferred.

The polymerization reaction preferably occurs in the liquid phase, andto this extent suificient pressure is employed to maintain anessentially liquid reaction mixture regardless Whether or not an inertnormally-liquid organic vehicle is employed. Preferably, thepolymerization reaction is conducted under an inert atmosphere, e.g.,nitrogen, butane, helium, etc. The ultimate molecular weight of theresulting polymer will depend, to an extent, upon various factors suchas the temperature, the choice and concentration of the catalyst, theuse and amount of an inert normally-liquid organic vehicle(s), and thelike.

In general, the reaction time will vary depending on the operativetemperature, the nature of the monomeric cyclic esters employed, theparticular catalyst and the concentr-ation employed, the use of an inertnormally-liquid organic vehicle, and other factors. The reaction timecan vary from several seconds to several hours, or more, depending onthe variables illustrated above.

It is preferred to conduct the polymerization reaction in the essentialabsence of impurities which contain active hydrogen since the presenceof such impurities tends to deactivate the catalyst and/ or increase theinduction period. The minimization or essential avoidance of impuritiessuch as water, carbon dioxide, aldehydes, ketones, etc., is highlydesirable. It is also preferred that the polymerization reaction beconducted under substantially anhydrous conditions.

When polymerizing an admixture containing at least two different cyclicesters, the proportions of said cyclic esters can vary over the entirerange. Broadly the concentration of each monomeric cyclic ester is inthe range of from about 3 to about 97 weight percent, based on the totalweight of said cyclic esters. The preferred range is from about 15. toabout 85 weight percent. Admixthres containing epsilon-caprolactone andmonoand/ or polyalkylsubstituted epsilon-caprolactone (includingisomeric mixtures thereof) are highly preferred as starting materials inthe process of the invention. Admixtures containing difierent monoand/or polyalkyl-substituted epsiloncaprolactones (including isomericmixtures of the same and/or different monoand/or polyalkyl-substitutedepsilon-caprolactones) also are highly preferred.

The polymers of this invention can be prepared via the bulkpolymerization, suspension polymerization, or

the solution polymerization routes. The polymerization reaction can becarried out in the presence of an inert normally-liquid organic vehiclesuch as, for example, aromatic hydrocarbons, e.g., benzene, toluene,xylene, ethylbenzcne, and the like; various oxygenated organic compoundssuch as anisole, the dimethyl and diethyl ethers of ethylene glycol, ofpropylene glycol, of diethylene glycol and the like; normally-liquidsaturated hydrocarbons including the open chain, cyclic, andalkyl-substituted cyclic saturated hydrocarbons such as hexane, heptane,various normally-liquid petroleum hydrocarbon fractions, cyclohexane,the alkylcyclohexanes, decahydronaphthalene, and the like. If desired, amixture of mutually miscible inert normally-liquid organic vehicles canbe employed.

The process of the invention can be executed in a batch,semi-continuous, or continuous fashion. The reaction vessel can be aglass vessel, steel autoclave, elongated metallic tube, or otherequipment and material employed in the polymer art. The order ofaddition of catalyst and monomeric reagent(s) does not appear to becritical. A suitable procedure is to add the catalyst to the reactionzone containing the monomeric reagent(s) and inert or,- ganic vehicle,if any. It is highly preferred that the catalyst be added as asuspension in an inert normallyliquid organic vehicle such as, forinstance, the normallyliquid saturated aliphatic and cycloaliphatichydrocarbons, e.g., hexane, heptane, octane, cyclopentane, cyclohexane,alkylcyclohexane, decahydronaphthalene, and the like. Incrementaladdition of catalyst to the reaction zone can be employed, If desired,the above procedure can be reversed, that is, the monomeric reagent(s)per se or as a solution or suspension in an inert organic vehicle can beadded to the reaction zone which preferably contains the catalyst as asuspension in an inert normally-liquid vehicle. Also, the catalyst,reagent(s), and inert organic vehicle, if any, can be added to thereaction zone simultaneously. The reaction zone (be it a closed vesselor an elongated tube) can be fitted with an external heat exchanger tothus control undue temperature fluctuations, or to prevent any possiblerun-away reaction temperatures due to the exothermic nature of thereaction. In a continuous operation employing as the reaction zone anelongated tube or conduit, the use of one or a plurality of separateheat exchangers can be conveniently used. In

a batch operation, stirring means can be provided for agitating thereaction mixture, as desired.

Unreacted monomeric reagent oftentimes can be recovered from thereaction product by conventional techniques such as by heating saidreaction product under reduced pressure. Removal of .unreacted monomericreagent(s) and/or inert organic vehicle can be accomplished bymechanical means such as treatment of the reaction product in a MarshallMill and the like. The polymer product also. can be recovered from thereaction product by washing said. reaction product with an such as byextrusion. The solid crystalline and noninert normally-liquid organicvehicle, e.g., heptane, and subsequently drying same under reducedpressure at slightly elevated temperatures. Another route involvesdissolution in a first inert organic vehicle, followed by the additionof a second inert organic vehicle which is miscible with the firstvehicle but which is a non-solvent for the polymer product, thusprecipitating the polymer product. If desired, the reaction product canbe dissolved in an inert organic vehicle such as acetone, and the like,followed by the addition of suiiicient water to the resulting solution,said water being miscible with said inert organic vehicle but being anon-solvent for the waterinsoluble polymer thereby precipitating thepolymer product. Recovery of the precipitated polymer can be effected byfiltration, decantation, etc., followed by drying same as indicatedpreviously.

The linearpolyester products resulting from the process of the inventioncan be characterized by the following recurring structural unit:

fills). filia wherein the variables R, A, x, y, and z, have the samevalues as shown in Formula I supra. Of course, the five provisosenumerated as (a) through (e) set forth in the discussion of Formula Isupra likewise apply to the structural unit designated as FormulaIII'above. In addition, as intimated previously, the molecular Weightsof the polyester products can range from about several hundred to aboutseveral thousand, e.g., from about 900 to about 100,000, and higher. Theultimate molecular weight and properties of the polyester products willdepend, in the main, upon the choice of the cyclic ester(s) andcatalyst, the concentration of the catalyst, the operative conditionsemployed, e.g., temperature, etc., the purity of the monomericreagent(s) and catalyst, the use and amount III 'of' an inertnormally-liquid organic vehicle, and the like.

It is readily apparent that the linear homopolymers are essentiallycharacterized by the same recurring unit which The polymers obtained bythe process of the invention are a useful class of polyester compounds.These polymers can range from viscous liquids to extremely tough,

crystalline solids. The polymers in the range of from very viscousliquids to relatively low molecular weight, wax-like solids are usefulin the preparation of cosmetics, polishes, and waxes, and as thickeningagents for various lubricants. The polymers can be employed to sizecellulosic material or they can be used as anti-static agents in thetreatment of fibrous materials. They can also be employed asprotectivecoatings and/or impregnants. The solid polymers are useful forthe production of various shaped articles such as brush handles,buttons, lamp bases, toys, and the like. The crystalline polymers can beshaped into useful fibers by conventional means crystalline polymersalso are useful in the preparation of films by such techniques asmilling on a two-roll mill,

calendaring, solvent casting, and the like.

In passing, it should be noted that one apparent advantage afforded bythe practice of the invention is the preparation of copolymers,terpolymers, etc., whose physical characteristics can be tailor-made tofit desired fields of applications and uses. In other words, byadjusting the concentration of the monomeric charge to a particularpolymerization system, copolymers, terpolym'ers, etc., which cover awide spectrum of properties and characteristics can be prepared, e.g.,soft, rubbery polymers to highly crystalline polymers.

In the illustrative operative examples to follow, the polymeric productoftentimes is described as possessing a certain reduced viscosity value.By this term, i.e., reduced viscosity, is meant a value obtained bydividing the specific viscosity by the concentration of the polymer inthe solution, the concentration being measured in grams of polymer per100 milliliters of solvent at a given temperature. The specificviscosity is obtained by dividing the difference between the viscosityof the solution and the viscosity of the solvent by the viscosity of thesolvent. The reduced viscosity value is an indication of the molecularweight of the polymer. Unless otherwise indicated, the reduced viscosityvalue was determined at 30 C.

Also, in the illustrative operative examples below, the polymerizationreaction was generally conducted under an inert atmosphere, e.g.,nitrogen. The reaction vessel and contents, i.e., cyclic ester(s),catalyst, and inert organic vehicle, if any, were maintained, usuallyunder agitation, in a constant temperature, e.g., 90 C., or the reactionvessel containing the cyclic ester(s) was maintained, usually underagitation, in a constant tempera ture and subsequently the catalyst wasadded thereto.

Since the polymerization reaction, in general, Was exothermic a rise intemperature was observed, e.g., 140 to 150 C. In several instances theperiod recorded was the time observed in which the rotation of themechanical stirrer ceased due to the high viscosity of the contents inthe reaction vessel. In most cases the reaction vessel was left in theconstant temperature bath for an additional period of time, e.g., about20 minutes, or longer. Unless otherwise indicated, the examination ordescription of the polymeric product was conducted at room temperature,i.e., about 23 C. In general, the conversion of monomer to polymer wassubstantially quantitative.

EXAMPLE 1 vA. To a reaction vessel maintained under a nitrogenatmosphere and which contained epsilon-caprolactone, there was chargedsodium methoxide in an amount so as to give an admixture containing 0.50weight percent sodium methoxide, based on the weight of saidepsiloncaprolactone. The reaction vessel then was placed in a constanttemperature bath maintained at 90 C. Within 30 minutes the mechanicalstirer ceased due to the high viscosity of the contents in the reactionvessel. Thereafter, the reaction product was dissolved in acetone andreprecipitated in water. There was obtained a solid polymer whichpossessed a reduced viscosity value of 0.36 (measured at 0.4 gram ofpolymer in 100 ml. of chloroform).

B. In an analogous manner as above, when S-hydroxyoctanoic acid lactoneis substituted for epsilon-caprolactone and contacted with 1.0 weightpercent potassium 2- ethylhexoxide, essentially similar results areobtained.

EXAMPLE 2 A. To a reaction vessel maintained under a nitrogen atmosphereand which contained epsilon-caprolactone, there was charged a suspensionof sodium methoxide in toluene in an amount so as to give an admixturecontaining 0.5 weight percent sodium methoxide, based on the weight ofsaid epsilon-caprolactone. The reaction vessel then was placed in aconstant temperature bath maintained at 90 C. Within 2 minutes themechanical stirrer ceased due to the high viscosity of the contents inthe reaction vessel. Thereafter, the reaction product was dissolved inacetone and reprecipitated in water. There was obtained a tough, solidhomopolymer which possessed a reduced viscosity value of 0.74 (measuredat 0.4 gram of polymer in 100 ml. of chloroform).

B. In an analogous manner as above, when beta,gam ma-dimethoxy-deltavalerolactone is substituted for epsilon-caprolactone and contacted with1.0 weight percent lithium phenoxide,-there is obtained a solid polymer.

EXAMPLE 3 A. To a reaction vessel maintained under a nitrogen atmosphereand which contained epsilon-caprolactone, there was charged a suspensionof sodium butoxide in toluene in an amount so as to give an admixturecontaining 0.5 weight percent sodium butoxide, based on the weight ofsaid epsilon-caprolactone. The reaction vessel then was placed in aconstant temperature bath maintained at C. Within 30 minutes themechanical stirrer ceased due 'to the high viscosity of the contents inthe reaction vessel. Thereafter, the polymer product was recovered.There was obtained a waxy homopolymer which possessed a reducedviscosity value of 0.4 (measured at 0.4 gram of polymer in m1. ofchloroform).

B. In an analogous manner as bove, when sodium allyloxide is substitutedfor sodium butoxide in an amount so as to give an admixture whichcontains 1.0 Weight percent of sodium allyloxide, based on the weight ofepsiloncaprolactone, essentially similar results are obtained.

EXAMPLE 4 A. To a reaction vessel maintained under a nitrogen atmosphereand which contains an isomeric mixture of methyl-epsilon-caprolactone,there is charged potassium phenethoxide in an amount so as to give anadmixture containing 0.5 weight percent potassium phenethoxide, based onthe total weight of methyl-epsilon-caprolactone. The isomeric mixturecontains, by weight, approximately 30 percentgamma-methyl-epsilon-caprolactone, about 30 percentepsilon-methyl-epsilon-caprolactone, and about 40 percent beta-methylanddelta-methyl-epsilon-caprolactone. This isomeric lactone mixture isprepared by reacting a mixture of 2-methyl-, 3-methyl-, and4-methylcyclohexanone with peracetic acid. The reaction vessel then isplaced in a constant temperature bath maintained at 90 C. for a periodof 2 hours. Thereafter, the polymeric-product is recovered. There isobtained a very viscous liquid product.

B. In an analogous manner as above, when 2-bromo-2- 3-rornopropyl)-5-hydroxypentanoic acid lactone is substituted for theisomeric mixture of methyl-3-epsiloncaprolactones and contacted with 1.0weight percent sodium alpha-naphthyloxide, substantially simlar resultsare obtained.

EXAMPLE 5 A. To a reaction vessel maintained under a nitrogen atmosphereand which contains an isomeric mixture composed of a mag'or proportionby weight of gammaoctyl-epsilon-caprolactone and a minor proportion byweight of epsilon-octyl-epsilon-caprolactone, there is chargedl-piperidylsodium in an amount so as to give an admixture containing 0.8weight percent n-l-piperidylsodium, based on the total weight ofoctyl-epsilon-caprolactone. The reaction vessel then is placed in aconstant temperature bath maintained at 90 C. for a period of 90minutes. Thereafter, the polymeric product is recovered. There isobtained a soft, solid polymer.

B. In an analogous manner as above, when 2,3, 1,5-tetrahydrobenzoxepin-Z-one issubstituted for the isomeric mixture ofoctyl-epsilon-caprolactones and contacted with 1.0 weight percent sodiumdodecoxide, substantially similar results are obtained.

EXAMPLE 6 A. To a reaction vessel maintained under a nitrogen atmosphereand which contains delta-valerolactone, there is charged lithiumn-butoxide in an amount so as to give an admixture containing 0.5 weightpercent lithium nbutoxide, based on the weight of saiddelta-valerolactone. The reaction vessel then is placed in a constanttempera- 11 ture bath maintained at 90 C. for a period of 45 minutes.Thereafter, the polymeric product is recovered. There is obtained atough, solid homopolyrner.

B. In an analogous manner as above, when 3-ethyl-2- keto-l,4 dioxane issubstituted for delta-valerolactone and contacted with 1.0 weightpercent sodium methylamide, a viscous liquid is obtained.

12 tholactone and contacted with 0.7 weight percent sodium'cyclohexoxide, essentially similar results are obtained.

EXAMPLES 12-13 In Examples 12 and 13 the procedure employed is similarto that set forth immediately preceding the operative examples. Thepertinent data and results are recorded in Table II below.

Table II Egrample Catalyst Temp., Time, Description of Number LactoneCharge Catalyst: Concen- O. Min. Polyester tration 30zeta-enantholactone/70 NaOCHa... 0.7 90 Tough,whitesolid.

epsilon-eaprolactone. 20 zeta-enantholactone/SO NaOOH;. 0.7 90 20 Do.

epsilon-caprolactone.

1 Admixture of two lactones is expressed as parts by weight. 2 Sodiummethoxide dispersed in the pane. 1 Weight percent catalyst, based ontotal weight of lactone charge.

N orE.Zeta enantholactone redistilled; B.P. 72 0. at 4 mm. of Hg; noot1.4689.

EXAMPLE 7 A. To a reaction vessel maintained under nitrogen atmosphereand which contains beta-methyl-delta-valerolactone (redistilled; boilingpoint 137 C. at 1.5 mm. of Hg; rz of 1.4480) there is charged potassiumdiethylamide in an amount so as to give an admixture containing 1.0weight percent potassium diethylamide, based on the weight of saidbeta-methyl-delta-valerolactone. The reaction vessel then is placed in aconstant temperature bath which is maintained at 90 C. for a period ofabout 40 minutes. Thereafter, the polymeric product is recovered. Thereis obtained a solid product.

B. In an analogous manner as above, when 3-oxa-6- hydroxyhexanoic acidlactone is substituted for beta-methyl-delta-valerolactone and contactedwith 0.6 weight percent sodium di-Z-ethylhexylamide, essentially similarresults are obtained.

EXAMPLES 8-10 In Examples 8 through 10, various copolymers are preparedby polymerizing an admixture of two lactones in the presence of sodiumisopropoxide. The procedure employed is similar to that set forthimmediately preceding the operative eXamples. The pertinent data andresults are recorded in Table I'below.

EXAMPLE 14 A. To a reaction vessel maintained under a nitrogenatmosphere and which contains 2-keto-1,4-dioxane, there is chargedlithium methoxide in an amount so as to give 'an admixture containing0.6 weight percent lithium methoxide, based on the weight of said2-keto-1,4-dioxane. The reaction vessel then is placed in a constanttemperaturebath maintained at 90 C. for a period of about 30 minutes.Thereafter, the polymeric product is recovered. There is obtained aslightly tough, solid polymer.

B. In an analogous manner as above, when gamma(lisopropyl 4methylcyclohexyl) epsilon caprolactone is substituted for2-keto-l,4-dioxane-and contacted with 1.0 weight percentl-pyrrolidylpotassium, there is obtained 'a viscous liquid.

EXAMPLES 15-16 'In Examples 15 and 16, various copolymers are preparedby contacting, at 90 C., a mixture of epsiloncaprolactone anddelta-valerolactone with 0.5 weight percent of sodium ethoxide, based onthe total weight of the lactone feed. The procedure employed is similarto that 'set forth immediately preceding the operative examples.

Table I Example Catalyst Temp., Tim Description of Number Laetone GhargeOoncen- 0. Min. Copolymer tration 8 70 epsilon-caprolaetone/30 betamethylo. 5 90 5 Hard solid.

delta-valerolactone. A 9 80 epsilon-caprolactone/20 beta-Inethyl- 0. 590 5 Tough, film-forming delta-valerolactone. solid. 10 85epsilon-eaprolaetonell5 beta-methyl- 0.5 90 10 Waxy solid.

delta-valerolactone.

Q 1 Parts by weight.

2 Weight percent catalyst, based on total weight of lactone charge.

No'rE.Beta-n1ethyl-delta-valerolaetone redistilled (13.1. of 137 C. at1.5 mm. of Hg; 1L1) of 1.4480).

EXAMPLE 11 droxyundecanoic acid lactone is substituted for zeta-enan Thepertinent data and results are recorded in Table III below.

Table III Ratio of Epsilon-Capro- Time, Description Example Numberlactone to Del- Min. of Copoly- V ta-Valerolacmer tone 1 15 20 14 Whitesolid. 16 80:20 7 Tough solid.

1 Ratio is in parts by weight.

13 EXAMPLE 17 A. To a reaction vessel maintained under a nitrogenatmosphere and which contains a mixture of 80 parts by weight ofepsilon-caprolactone and 20 parts by weight of mixeddimethyl-epsilon-caprolactones, there is charged sodium anilide in anamount so as to give an admixture containing 0.5 weight percent sodiumanilide, based on the total Weight of the lactone feed. The mixeddimethylepsilon-caprolactones is an isomeric mixture of beta,gamma-dimethyland gamma,delta-dimethyl-epsilon-caplactones. The reactionvessel'then is placed in a constant temperature bath maintained at 90 C.for a period of 1.5 hours. Thereafter, the polymeric product isrecovered. There is obtained a soft, solid product.

B. In an analogous manner as above, when equal parts by weight ofl2-oxa-lS-hydroxypentadecanoic acid lactone and 7-hydroxyheptanoic acidlactone are employed as the monomeric feed and contacted with 1.0 weightpercent potassium N-phenyl-ethylamide, substantially similar results areobtained.

EXAMPLE 18 A. To a reaction vessel maintained under a nitrogenatmosphere and which contains a mixture of 50 parts by weight ofepsilon-caprolactone and 50 parts by weight of mixedoctyl-epsilon-caprolactones, there is charged lithium nbutoxide in anamount so as to give an admixture containing 0.5 weight percent lithiumn-butoxide, based on the total weight of the lactone feed. The mixedoctyl-caprolactones comprised a major proportion by weight ofgamma-octyland a minor proportion by weight ofepsilon-ctyl-epsilon-caprolactones. The reaction vessel then is placedin a constant temperature "bath maintained at 90 C. for a period of 30minutes. Thereafter, the reaction product is dissolved in acetone andreprecipitated in water. There is obtained a waxy copolymer.

B. In an analogous manner as above, when equal parts by weight of9-oxabicyclo [5.2.2]undecan-8-one and 1,4-dioxane-2-one are employed asthe monomeric feed and contacted with 1.5 weight percent potassiumn-butoxide, essentially similar results are obtained.

EXAMPLE 19 EXAMPLE 20 A. To a reaction vessel maintained under anitrogen atmosphere and which contained ortho-(2-hydroxyethyl)-phenylacetic acid lactone, there is charged lithium diisopropylamide'inan amount so as to give an admixture containing 0.50 weight percentlithium diisopropylamide, based on the weight of saidortho-(2-hydroxyethyl)- phenylacetic acid lactone. The reaction vesselthen is placed in a constant temperature bath maintained at 90 C. for 30minutes. Thereafter, the polymeric product is recovered. There isobtained a solid polymer.

B. In an analogous manner as above, whencis-3-oxabicyclo[5.4.0]undecan-4-one is substituted for ortho-(2-hydroxyethyl)-phenylacetic acid lactone and contacted with 1.0 weightpercent potassium phenoxide, essentially similar results are obtained,

EXAMPLE 21 A. To a reaction vessel maintained under a nitrogenatomsphere and which contained delta-valerolactone, there was chargedlithium n-butoxide in an amount so as to give an admixture containing0.5 weight percent lithium n-butoxide, based on the weight of saiddeltavalerolactone. The reaction vessel then was placed in a constanttemperature bath maintained at C. Within 3 minutes the mechanicalstirrer ceased due to the high viscosity of the contents in the reactionvessel. Thereafter, the polymeric product was recovered. There wasobtained a polymeric product which possessed a reduced viscosity valueof 0.39 (measured at 0.4 gram of polymer in m1. of chloroform). Theyield was about 78 percent.

B. In an analogous manner as above, when gamrna(lisopropyl 4methylcyclohexyl)-epsilon-caprolactone is substituted fordelta-valerolactone and contacted with 0.7 weight percent sodium2-propylphenoxide, a viscous liquid product is obtained.

EXAMPLE 22 To a reaction vessel maintained under a nitrogen atmosphereand which contained epsilon-caprolactone, there was charged lithiumdiethylamide in an amount so as to give an admixture containing 0.5weight percent lithium diethylamide, based on the weight of saidepsilon-caprolactone. The reaction vessel then was placed in a constanttemperature bath maintained at 90 C. Within 1.5 minutes the mechanicalstirrer ceased due to the high viscosity of the contents in the reactionvessel. Thereafter, the polymer was recovered. There Was obtained atough, crystalline, solid homopolymer which possessed a reducedviscosity value of 0.79 (measured at 0.2 gram of polymer in 100 ml. ofchloroform).

EXAMPLE 23 To a reaction vessel maintained under a nitrogen atmosphereand which contained 50 parts by weight of delta-valerolactone and 50parts by weight of beta-methyl-delta-valerolactone, there was chargedlithium diethylamide in an amount so as to give an admixture containing0.5 weight percent lithium diethylamide, based on the weight of thetotal lactone feed. The reaction vessel then was placed in a constanttemperature bath maintained at 90 C. Within one minute the mechanicalstirrer ceased due to the high viscosity of the contents in the reactionvessel. Thereafter, the polymer was recovered. There was obtained a veryviscous yellow liquid.

Although the invention has been illustrated by the preceding examples,the invention is not to be construed as limited to the materialsemployed in the above exemplary examples, but rather, the inventionencompasses the generic area as hereinbefore disclosed. Variousmodifications and embodiments of this invention can be made withoutdeparting from the spirit and scope thereof.

What is claimed is:

l. A process which comprises polymerizing a cyclic ester characterizedby the following formula:

wherein each R, individually, is selected from the group consisting ofhydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl, halo, haloalkyl,alkoxyalkyl, alkoxy, aryloxy, a portion of an aromatic hydrocarbonnucleus which nucleus is fused to the cyclic ester ring, and a portionof a saturated cycloaliphatic hydrocarbon nucleus which nucleus containsfrom 4 to 10 carbon atoms and which is fused to the cyclic ester ring;wherein A is selected from the group consisting of an oxy group, a thiogroup, and a divalent saturated aliphatic hydrocarbon group, wherein xis an integer in the range of from 1 to 15 inclusive; wherein y is aninteger in the range of from 1 to 15 inclusive;

ceed 18, and (c) the total number of organic'substituents attached tothe carbon atoms contained in the cyclic ester n'ng does not exceedfour; with from about 0.001 to about weight percent, based on the totalweight of cyclic ester, of a compound characterized by the followingformula:

wherein M is selected from the group consisting of lithium, sodium,potassium, rubidium and cesium; and

'wherein A is selected from the group consisting of 1- piperidyl,l-pyrrolidyl, l-pyrryl, N-carbazolyl, and the unit wherein each Rindividually, is selected from the group consisting of hydrogen and amonovalent hydrocarbon radical; under substantially anhydrousconditions; for a period of time sufiicient to produce a polymer.

2. 'A process which comprises polymerizing an admixture comprising atleast two cyclic esters which are characterized bythe following formula:

cleus is fused to the cyclic ester ring, and a portion of a saturatedcycloaliphatic hydrocarbon nucleus which nuoleus contains from 4 to 10carbon atoms and which is fused to the cyclic ester ring; wherein A isselected from the group consisting of an oxy group, a thio group, and

.a divalent saturated aliphatic hydrocarbon group; wherein x isanjinteger in the range of from '1 to inclusive; wherein y is an integerin the range of from 1 to 15 inclusive; and wherein z is an integerselected'from the group consisting of zero and one; with the provisosthat (a) the sum of x+y+z cannot equal three, (b) the total number ofatoms forming the cyclic ester ring does not exceed 18, and (c) thetotal number of organic substituents attached to the carbon atomscontained in the cyclic ester ring does not exceed four; with from about0.001 to about 10- weight percent, based on the total weight of. cyclicester, of a compound characterized by the following formula:

wherein M is selected from the group consisting of lithium, sodium,potassium, rubidium and cesium; and wherein A is selected from the groupconsisting of 1- piperidyl, l-pyrrolidyl, l-pyrryl, N-carbazolyl, andthe unit percent, based on the weight of said delta-valerolactone,

of an alkylamide of a metal, said metal being selected from the groupconsisting of lithium, sodium, potassium,

16 rubidium, and cesium; at a temperature in the range of from about--20 C. to about 225 C.; under substantially anhydrous conditions; andfor a period of time sufiicient to produce a polymer.

4. A process which comprises polymerizing an alkylsubstituteddelta-valerolactone with from about 0.01 to about 3.0'weight percent,basedon the weight of said alkyl-substituted delta-valerolactone, of analkylamide of a metal, said metal being selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium; at atemperature in the range of from about I 20 C. to about 225 C.; undersubstantially anhydrous conditions; and fora period of time sufiicientto produce a polymer.

5. A process which comprises polymerizing epsiloncaprolactone withfromabout 0.01 to about 3.0 weight percent, based on the weight of saidepsilon-caprolactone, of an alkylamide of a metal, said metal beingselected from the group consisting of lithium, sodium, potassium,rubidium, and cesium; at a temperature in the range of from about 20 C.to about 225 C.; under substantially anhydrous conditions; and for aperiod of time sufiicient to produce a polymer.

6. A process which comprises polymerizing an alkylsubstitutedepsilon-caprolactone with from about 0.01 to about 3.0 weight percent,based on the weight of said 'alkylsubstituted epsilon-caprolactone, ofan alkylamide weight of the monomeric lactone feed, of an alkylamide ofa metal, said metal being selected from the group consisting of lithium,sodium, potassium, rubidium, and cesium; at a temperature in the rangeof from about -20 C. to about 225 C.; under substantially anhydrousconditions; and for a. period of time sufiicient to produce a polymer. s

8. A process which comprises polymerizing a monomeric lactone admixturecomprising delta-valerolactone and epsilon-caprolactone with from about0.01 to about 3.0 weight percent, based on the total weight of themonomeric lactone feed, of an alkylamide of a metal, said metal beingselected from the group consisting of lithium, sodium, potassium,rubidium, and cesium; at a temperaturein the range of from about 20 C.to about 225 (3.; under substantially anhydrous conditions; and for aperiod of time suflicient to produce a polymer.

9. A process which comprises polymerizing a monomeric lactone admixturecomprising delta-valerolactone and an alkyl-substitutedepsilon-caprolactone with from about 0.01 to about 3.0 weight percent,based on the total weight of the monomeric lactone feed,,of analkylamide ofa metal, said metal beingselected from the group consistingof lithium, sodium, potassium, rubidium, and cesium; at a temperature inthe range of from about 20 C. to about 225 C.,.under substantiallyanhydrous conditions; and for a period of time suflicientto produce apolymer.

10. A process which comprises polymerizing a monomeric lactone admixturecomprising epsilon-caprolactone and an alkyl-substituteddelta-valerolactone with from about 0.01 to about 3.0 weight percent,based on the total weightof the monomeric lactone feed, of an alkylamideof a metal, said metal being-selected from the group con sisting oflithium, sodium, potassium, rubidium, and cesium; at a temperature inthe range of from about 20 C. to, about 225 C., under substantiallyanhydrous 17 conditions; and for a period of time sufficient to producea polymer.

11. A process which comprises polymerizing a monomeric lactone admixturecomprising epsilon-caprolactone and an alkyl-substitutedepsilon-caprolactone with from about 0.01 to about 3.0 weight percent,based on the total weight of the monomeric lactone feed, of analkylamide of a metal, said metal being selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium; at atemperature in the range of from about 20 C. to about 225 C.; undersubstantially anhydrous conditions; and for a period of time sufiicientto produce a polymer.

12. A process which comprises polymerizing a monomeric lactone admixturecomprising an alkyl-substituted epsilon-caprolactone and analkyl-substituted delta-valerolactone with from about 0.01 to about 3.0weight percent, based on the total weight of the monomeric lactone feed,of an alkylamide of a metal, said metal being selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium; at atemperature in the range of from about 20 C. to about 225 C.; undersubstantially anhydrous conditions; and for a period of time sufiicieutto produce a polymer.

13. A process which comprises polymerizing a mono- 2 men'c lactoneadmixture comprising two alkyl-substituted delta-valerolactones withfrom about 0.01 to about 3.0

weight percent, based on the total weight of the monomeric lactone feed,of an alkylamide of a metal, said metal being selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium; at atemperature in the range of from about 20 C. to about 225 C.; undersubstantially anhydrous conditions; and for a period of time sufiicientto produce a polymer.

14. A process which comprises polymerizing a monomeric lactone admixturecomprising two alkyl-substituted epsilon-caprolactones with from about0.01 to about 3.0 Weight percent, based on the total Weight of themonomeric lactone feed, of an alky-lamide of a metal, said metal beingselected from the group consisting of lithium, sodium, potassium,rubidium, and cesium; at a temperature in the range of from about 20 C.to about 225 C.; under substantially anhydrous conditions; and for aperiod of time suflicient to produce a polymer.

References Cited in the file of this patent UNITED STATES PATENTS2,809,958 Barnes et a1 Oct. 15, 1956 2,848,441 Reynolds Aug. 19, 1958FOREIGN PATENTS 766,347 Great Britain Ian. 23, 1957 775,495 GreatBritain May 22, 1957

1. A PROCESS WHICH COMPRISES POLYMERIZING A CYCLIC ESTER CHARACTERIZED BY THE FOLLOWING FORMULA: 